This invention relates to a scintillation detector for three-dimensionally measuring the position of gamma-ray absorption in the detector, and a positron computed tomography (CT) apparatus including plural scintillator detectors arranged in the form of a ring for uniformly obtaining high resolution over the region from the center to the periphery of a visual field without degradation of the spatial resolution in the peripheral region of the visual field.
In nuclear medical diagnosis, a drug labeled with a radioactive isotope (hereinafter referred to as an "RI") is ingested by or injected into a patient, and gamma-rays emitted from the RI in the patient's body are detected outside of the body, thereby providing the distribution of the RI within the body and enabling diagnosis of metabolic functions of internal organs of the body. It is important that the drug labeled with the RI accurately represents the metabolic functions of particular internal organs in the body. For example, where a particular RI is not an inherent element in a living body, a drug labeled with that RI causes metabolic activity and metabolic processes to be significantly changed in comparison with a drug which is not labeled, so that subsequent search for or investigation of the metabolic function is frequently difficult.
A living body is composed of elements including H, C, N and O. These elements also contribute to the metabolism of the living body. A drug labeled with a positron emitter such as .sup.11 C, .sup.13 N, .sup.15 O, or the like, can accurately represent the metabolic function because substances participating in the metabolism, such as C, N, O and the like, are merely replaced by their isotopes and as a result no change is made in chemical structure. Therefore, positron CT for detecting positron nuclides is useful in the field of nuclear medical diagnosis.
FIG. 9 shows a conventional gamma-ray detector employed in a conventional positron CT apparatus. FIG. 9(A) shows a gamma-ray detector comprising a number of scintillators 1 arranged in the form of a ring and photodetectors 2 connected to the scintillators at a ratio of one to one. FIG. 9(B) shows a detector in which scintillators 1 are connected to photodetectors 2 at a ratio of N scintillators to one photodetector, where N is an integer. FIG. 9(C) shows a gamma-ray detector comprising cylindrical scintillators 1 and photodetectors 2 connected to both sides or ends of the scintillators.
In a positron CT apparatus having a gamma-ray detector as described above, two of the scintillators arranged in the form of a ring simultaneously detect two gamma-rays propagating in opposite directions which are radiated when positrons emitted from the RI combine with electrons and are thereby annihilated. A distribution of RIs on a circular plane (hereinafter referred to as "as visual field") defined by the scintillators arranged in the form of a ring can then be observed.
The positron CT apparatus as described above has disadvantage in that spatial resolution is degraded in a peripheral region of the visual field of the apparatus. Moreover, this disadvantage becomes more pronounced as individual scintillators are designed to be narrower to increase their resolving power and longer to increase gamma-ray detection efficiency and sensitivity. Such a problem is caused by the structure and arrangement of the scintillators.